The present invention relates generally to the field of marine geophysical surveying. More particularly, in one or more embodiments, this invention relates to methods and systems for using an impact-activated device for repelling sharks from marine geophysical survey equipment.
Certain types of marine geophysical surveying, such as seismic or electromagnetic surveying, include towing an energy source at a selected depth in a body of water. One or more geophysical sensor streamers also may be towed in the water at selected depths. The streamers are essentially long cables having geophysical sensors disposed thereon at spaced apart locations. The energy source and streamers may be positioned in the water by attached equipment, such as deflectors and inline position control devices. Actuation of the energy source emits an energy field into the body of water. The energy field interacts with the rock formations below the water bottom. Energy that interacts with interfaces, generally at the boundaries between layers of rock formations, is returned toward the surface and is detected by sensors on the one or more streamers. The detected energy is used to infer certain properties of the subsurface rock, such as structure, mineral composition and fluid content, thereby providing information useful in the recovery of hydrocarbons. Some types of marine geophysical surveying utilize ocean bottom cables, arrays, and/or nodes for locating the geophysical sensors in the water.
One problem that has been encountered in marine geophysical surveying is damage caused by sharks biting the marine geophysical survey equipment. While shark-repelling techniques ranging from semio-chemicals and surfactants to electrical have been used to drive sharks from an area, these techniques have been mainly used to repel sharks from divers. One current electrical device designed to repel sharks from divers is SharkShield™ shark deterrent system, commercially available from Shark Shield Pty Ltd of Brompton, South Australia. Because this system emits high-voltage pulses continuously into the water, its battery life is limited to about one hour, making it unsuitable for protection of towed equipment in a geophysical survey.
Accordingly, there is a need for methods and systems for protection of equipment in marine geophysical surveys from shark bites.